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Trio of intense spacewalks set to begin

Canadian astronaut Steve MacLean is lowered into the Neutral Buoyancy Laboratory at Johnson Space Center in Texas, US, to practice a spacewalk

(Image: NASA)

It will take three spacewalks and four of the space shuttle Atlantis’s six astronauts to attach a massive new truss segment to the half-built International Space Station (ISS) – making Atlantis the most complicated ISS construction mission yet.

It carried up a 16-tonne truss segment that will lengthen the station’s “spine”. The P3/P4 segment bears two solar arrays that will double the station’s power production capability.

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Installing the massive structure will require three spacewalks, each lasting 6.5 hours. Crew members Joe Tanner and Heidemarie Stefanyshyn-Piper will make two of the spacewalks, with the first beginning on Tuesday.

Tanner is a spacewalking veteran who will be making his sixth and seventh spacewalks on this mission. “This is kind of a coming home for me,” Tanner says. He conducted very similar spacewalks on his most recent space shuttle flight in 2000, in which the station’s first US solar arrays were added.

Size matters

Stefanyshyn-Piper, on the other hand, will be making her first spacewalk, or Extra-Vehicular Activity (EVA) in NASA parlance. In so doing, she will become only the seventh American woman to do an EVA. A Soviet woman walked in space in 1984.

So few women have gone on EVAs in part because the existing US space suits are too large for most women. The smallest available size is a medium, roughly equivalent to a men’s medium T-shirt.

Smaller arms can be attached to the suit’s torso, but often the torso itself is simply too big. “If the [suit’s shoulder] is halfway down your upper arms, obviously you’re going to have a harder time working in the suit,” Stefanyshyn-Piper told New Scientist. Stefanyshyn-Piper stands 178 centimeters (5 foot, 10 inches) tall, enabling her to fit into a medium-sized suit better than most women.

In addition to the suits themselves, the gloves astronauts wear in space are also usually too big for most women. While NASA can send up smaller gloves, the gloves become stiffer as they get smaller, making it difficult to accomplish the many detailed tasks required on spacewalks.

Umbilical lines

To prepare for the spacewalks, astronauts run through these tasks in a giant swimming pool called the Neutral Buoyancy Laboratory. Initially, spacewalking newbie Stefanyshyn-Piper had to work very hard to keep pace with her seasoned partner Tanner during these practice sessions. “Keeping up with Joe is no small feat in the pool,” says Atlantis commander Brent Jett.

But after four years of training, Tanner and others say she can now hold her own. “She is in my opinion one of the best that we have – flown or unflown,” Tanner says. “I’d stack her against anybody, and you’ll see her [on an EVA] again.”

To prepare for the first spacewalk, the crew used the shuttle’s Canadian-built robotic arm on Monday to take the P3/P4 truss out of the shuttle’s payload bay and hand it over to the station’s robotic arm, which will attach the segment to the space station.

At 0515 EDT (0915 GMT) on Tuesday, Tanner and Stefanyshyn-Piper will step out into space. They will then begin the laborious task of attaching 13 umbilical lines from the station’s existing P1 truss segment to its new P3/P4 segment.

This process requires an exceptional amount of back-and-forth communication and cooperation between the spacewalkers and ground controllers. “From my perspective, EVA 1 is probably the most choreographed between the ground and crew,” says John McCullough, the station’s lead flight director. “Once EVA 1 is complete, I’ll feel a little bit better.”

Extended mission

Near the end of the spacewalk, Stefanyshyn-Piper will install the motors that drive a rotating joint on the truss, called the Solar Alpha Rotary Joint (SARJ). The joint will eventually rotate to keep the solar arrays constantly pointed towards the Sun. They will also position the boxes holding the solar arrays, which will be deployed after the second spacewalk of the mission.

On Wednesday, Canadian astronaut Steve MacLean and US astronaut Dan Burbank will make that spacewalk, paving the way for the solar array deployment.

Because the deployment is so crucial, their spacesuits will be supplied with lithium hydroxide to remove the carbon dioxide they exhale, allowing them to work an extra half hour if necessary. “They have quite a task in front of them,” says John Haensly, lead spacewalk officer for this flight.

MacLean, who will become the second Canadian to perform an EVA, said that the night before his first spacewalk will feel like Christmas Eve to a child. “There’s no question I’ll be thinking about [the EVA] as I fall asleep,” MacLean says.

The pair will spend most of their day around the SARJ, removing locks and restraints that held parts of the truss secure during the vibrations of launch. They will take along extra batteries for the drill they will need for many of the tasks.

Radiator installation

On Friday, Tanner and Stefanyshyn-Piper will embark on their second 6.5-hour foray outside the station. Their main mission this time around will be to deploy a radiator that will help cool the new truss segment. They will also continue removing the launch restraints; repair an S-band communications antenna on the station’s S1 truss; and retrieve a suitcase-shaped experiment called MISSE-5, which had exposed 200 different materials to the harsh conditions of space.

So far, the orbiter appears to have survived launch without sustaining any major damage to its heat shield from ice or foam falling off its external fuel tank.

But should any damage be discovered, NASA could also attempt a repair on one of their spacewalks, using one of several experimental techniques tested on the past two shuttle flights (see Spacewalking astronauts testing heat shield repairs). Tanner would likely be on that EVA because of his extensive spacewalking experience.